Exploring the roles of ocean circulation and orbital forcing on palaeoceanographic conditions in the southern Tethys during the Late Cretaceous

For much of Earth history atmospheric CO2 levels and average global temperatures are thought to have been much higher than present. These periods of time are known as 'greenhouse' climates. The Cretaceous (145 to 65 million years ago) was an extreme end-member of a greenhouse climate. Then the climate was much warmer than it is today; there was little or no polar ice and sea-levels were high. In polar areas, like Alaska and Antarctica, which are cold today, dinosaurs, crocodiles and tropical plants flourished. The Cretaceous ocean was also sensitive to changes in oxygen concentration, and, at times, became completely devoid of oxygen over widespread areas (so-called 'oceanic anoxic events' or OAEs). The controls on Cretaceous warmth and the links between the greenhouse climate and short-duration events, such as OAEs, are not well understood. Two factors are likely to have been important over different timescales. Over long-timescales (millions of years), changes in atmospheric carbon dioxide and the position of the continents are major drivers of climate. The positions of the continents can affect patterns of ocean circulation, which control the movement of heat around the Earth surface, and the storage of heat in the interior of the ocean. In the modern world, surface water sinks to great depths in the oceans in high-latitude regions and then fills the deepest parts of the ocean basins. This formation of deep-water masses provides oxygen throughout much of the ocean. However, in times of extreme warmth, such as the Cretaceous, it is uncertain whether these processes were operational, with implications for both climate and ocean environments. Using the new deep-sea sediment cores collected during Expedition 369, this project will use an element (neodymium) as a tracer for deep-water masses in the Late Cretaceous, which will allow us to determine where deep-water was coming from (high or low latitudes?), whether these sources changed through time as the continents moved and the relationships between water mass sources and other climatic and environmental phenomena, such as OAEs.

On shorter-time scales of 10s to 100s of thousands of years, climate is controlled by variations in Earth's orbit. These variations effect the seasonal and geographic distribution of energy from the sun and the total amount of energy the planet receives, all of which can lead to climatic oscillations. Investigating the signature of these climatic cycles can help understand which processes on Earth were important in controlling regional climates in the past. Furthermore, because each cycle type has a characteristic duration, counting cycles can be used to determine the amount of time represented by a given thickness of sediment on the sea floor. This in turn can help refine the geological time scale by providing accurate estimates of the amount of time that elapsed between key points in the geological record, such as the evolution and extinction of certain organisms. This project will make measurements of the chemical and physical characteristics of the sediment cores from Expedition 369 at extremely high-resolution (more than 50 measurements per m) over 10s to 100s of meters. These data can then be analysed to determine how many cycles are present and of what type.

The proposed research will benefit interested academics, people in the hydrocarbon industry, educationalists and the general public. The named PDRA will also benefit.

Academics will benefit from the provision of new data from a little-studied area of the world. These data may be used to enhance existing models and ideas of how the Earth System operated during the Cretaceous and, thus, are of relevance to understanding how the climate system works more broadly. Additionally, the proposed research may lead to a refinement of the geological timescale, which is of benefit to everyone working on the Mesozoic Era of Earth's history. Academics will be engaged with via academic conferences and publications.

The hydrocarbon industry will be interested in the outcomes of the research as they will provide insights into the controls on ocean chemistry during the Cretaceous that led to the formation of organic-rich deposits, which ultimately become hydrocarbons in some settings. The revision of the geological timescale is also useful to this group in terms of stratigraphic correlations and constraining the timing of events such as tectonic movements, basin history, and hydrocarbon development. This group will be engaged with primarily through the academic literature and conferences.

Educationalists and the general public are often interested in scientific drilling as an endeavour in itself and palaeoclimate research. We will engage with these groups via the outreach activities of IODP and UKIODP (including live broadcasts from the ship) and through the schools outreach work of the Department of Earth Sciences in Oxford.

The PDRA will benefit from developing her skills in project management and scientific independence.